KR102048059B1 - Process for washing dinitrotoluene - Google Patents

Abstract

The present invention provides a process for washing a crude mixture comprising dinitrotoluene, nitric acid, nitrogen oxides and sulfuric acid obtained from the nitration of toluene after separating nitro-acid, comprising two washing steps (WS-I) and (WS- II), where
i) In a first cleaning step (WS-I), the crude mixture is extracted with a cleaning acid I comprising nitric acid, nitrogen oxides and sulfuric acid by a cleaning comprising at least one extraction stage, wherein the first cleaning step (WS-I) The washing acid discharged from the first extraction stage (WS-I-1) of I) has a total acid content of 20 to 40% by weight, and a pre-cleaned crude mixture is obtained.
ii) In a second washing step (WS-II), the pre-cleaned crude mixture comprising dinitrotoluene is extracted with washing acid II by washing comprising at least one extraction stage, wherein the second washing step (WS-II) The washing acid discharged from the first extraction stage (WS-II-1) of II) relates to a method of obtaining a mixture comprising dinitrotoluene having a pH of 4 or less and substantially free of nitric acid, sulfuric acid and nitrogen oxides. .

Description

Cleaning method of dinitrotoluene {PROCESS FOR WASHING DINITROTOLUENE}

The present invention relates to a process for washing a crude mixture comprising dinitrotoluene (DNT), nitric acid, nitrogen oxides and sulfuric acid obtained after the separation of nitric acid from nitration of toluene.

In particular, the present invention provides sulfuric acid, which enables biological treatment in a water treatment plant after removal of DNT dissolved in water, either directly or by extraction, for the resulting wash water from this wash, without further physical or chemical pretreatment. And a process for washing DNT-comprising crude mixture (hereinafter also referred to as crude DNT) from continuous isothermal nitration of toluene to form DNT in a mixture of nitric acid, wherein the wastewater flowing out of the water treatment plant is, for example, Waste water regulation, Annex 22: Cleaning methods that meet the requirements in terms of toxicity as defined in Chemische lndustrie.

In continuous isothermal or adiabatic nitration of toluene to form DNT in one or two stages with mixed acid and countercurrent, the crude nitroaromatic product is always obtained after phase separation, which removes impurities dissolved therein before further use. Should be. Oxidation products from secondary reactions with aromatics, such as mononitrocresol, which should be nitrated, apart from the final nitric acid consisting of nitric acid, sulfuric acid and nitrogen oxides present in the nitroaromatic product as a fine emulsion or in dissolved form. Dinitrocresol and trinitrocresol, or aromatic carboxylic acids such as mononitrobenzoic acid and dinitrobenzoic acid (hereinafter referred to as nitrobenzoic acid or NBA) and degradation products thereof are also included in the crude DNT.

In the prior art, these impurities are removed from the crude product by multistage washing before the nitroaromatic product is used directly, through isomer separation or hydrogenation, to form the corresponding amine.

A crude nitroaromatic product, such as DNT, is a cleaning in which removal of the dissolved and suspended acid in it is carried out of nitration mixtures, nitrocresol and other acids and generally additional impurities that can be extracted by the cleaning medium. (F. Meissner et al in Industrial and Engineering Chemistry Vol 46, 721 (1954), Ullmanns Enzyklopiidie der technischen Chemie, 4 ^th edition, Vol. 17, pp. 385-386; H. Hermann et al in ACS-Symposium Series 632 238 (1996) page 241; ed. LF Albright, RVC Carr, RJ Schmitt, US 6 288 289, EP 1 816 117) comprises three steps:

1. cleaning (acid cleaning) to remove dissolved and suspended minerals such as sulfuric acid, nitric acid and nitrogen oxides;

2. Sodium carbonate (soda), for removal of degradation products such as oxalic acid from oxidative degradation of weakly acidic impurities such as nitrocresol, nitrobenzoic acid and nitrocresol or oxidative degradation of aliphatic or cyclic hydrocarbons, dissolved in crude nitroaromatic products, Washing in the presence of a base such as sodium bicarbonate, ammonia, sodium hydroxide, potassium hydroxide and the like (see US 4 482 769, US 4 597 875, US 6 288 289);

3. Neutral cleaning to remove traces of residual alkali and further reduce traces of impurities remaining in the product.

Water is generally used as the cleaning medium for this purpose, and the cleaning is performed as a liquid / liquid cleaning at a temperature at which the nitroaromatic product to be cleaned is present as a liquid.

The purpose of these rinsing is to achieve not only pure but also waste water per metric ton of product which achieves as little product as possible and the level of rinsed impurities in the waste water which enables the disposal of the impurities carried out at high cost.

Thus, three different wastewater streams are obtained from the washing of crude DNT, namely wastewater from acid washing, alkali washing and neutral washing.

In the case of DNT, the waste water from the acid rinse, for example, employs the processes described in EP 0 736 514 and EP 1 780 195, with sulfuric acid, nitric acid and sulfuric acid dissolved in the crude product in an amount of 25 to 40% by weight total acid. An amount of up to 0.5% by weight (corresponding to its solubility) with mineral acids such as nitrous acid and only other traces of less acidic nitrophenols, nitrocresols, nitrobenzoic acid or other organic acids such as oxalic acid (from oxidative degradation by nitric acid) ) Includes the dissolved product. The TOC of this wastewater is surprisingly high, about 8-9000 mg / l, less than 50% of which is produced from DNT dissolved in the wash acid.

Wastewater from alkaline cleaning has a pH above 9 and, for DNT, about 500-5000 ppm of nitrate, 500-5000 ppm of nitrite and up to several hundred ppm of sulfate with substantially 1300 ppm of dissolved product Include. Corresponding to its solubility, the phenolic nitro compound dissolved in the crude product comprises up to 800 ppm of nitrocresol, up to 800 ppm of nitrobenzoic acid, and traces of cyanide from oxidative degradation of nitrocresol ( See US 4 361 712). The TOC in this alkaline wash water from the DNT wash is 1500-3200 mg / l. Only up to 50% of this TOC is produced from NBA and nitrocresol dissolved in waste water. The remainder is unknown and probably came from the oxidation product of nitrocresol in the DNT stage. Alkaline wastewater generally has a dark color ranging from strong orange to reddish brown.

Wastewater from the neutral wash may be slightly alkaline or slightly acidic at pH 3-8, depending on how much entrained from the preceding wash stage (alkaline wash) and which base is used in the alkaline wash. Apart from the product dissolving at a saturation corresponding to its solubility at the cleaning temperature employed, the wastewater from the neutral cleaning contains traces of residual base used for alkaline cleaning, and impurities still remaining in the DNT, mainly nitrocresol. do.

In order to minimize the amount of water required for this washing, in alkaline washing, after addition of a base, washing is performed in countercurrent while employing water used for neutral washing (AB Quakenbush et. Al., The Olin Dinitrotoluene ( DNT) Process, Polyurethane World Congr. Proc. 1993, Publish .: Technomic Lancaster, p. 485), or directly or after further enrichment as described in EP 0 279 312, EP 0 736 514 and EP 1 780 195. An acid wash is performed using a minimum amount of water to provide a concentrated acid that can be recycled to nitration.

Wastewater from the plant for the nitration of toluene to form the DNT, washing water from the washing of the crude DNT and steam condensate from the final acid and the concentration of the washing acid can be discharged. In order to achieve the applicable emission parameters set downward in the FRG's wastewater regulations for COD, nitrogen, heavy metals and biological parameters, complex treatments have to be carried out prior to introduction.

The wastewater stream in need of treatment from the nitration plant is always from steam condensate from concentration of the final nitric acid (referred to as SAC wastewater), and from washing with base, especially in the pH range of 7-10. Is wastewater. As far as possible all toxic, genotoxic or bacteriostatic substances and also all inorganic salts, in particular nitrates and nitrites, from these wastewater streams, in order to meet defined emission parameters, before discharge to the effluent discharge duct. Should be removed.

In particular from the rinsing of DNT with a base comprising soluble nitro compounds, nitrobenzoic acid and other organic acids in dissolved content in an amount of up to 0.5% corresponding to solubility, and low molecular weight decomposition products dissolved in the crude product. Wastewater requires high expenditure for the removal of nitroaromatic and phenolic impurities and other impurities of toxicity, carcinogenicity, mutagenicity and bacterial growth inhibition.

A number of different methods have been described for removing these toxic substances from alkaline wash water prior to discharge.

Apart from the purely mechanical separation of nitrocresol from the wastewater of the DNT washing with base, in particular sodium carbonate, the wastewater is passed from the main product nitro molecule, especially from the wastewater, and / or Process for treatment with activated carbon or ion exchange resins to remove or reduce the amount of phenolic nitro molecules such as dinitrophenol and trinitrophenol (picrinic acid) and dinitrocresol and trinitrocresol (TNC) in waste water, Extraction processes to aromatics to be nitrated, treatment with oxidants such as ozone or fenton reagents, or treatments at high temperatures up to 300 ° C are described.

US 4 597 875 describes a process for the removal of, in particular, toxic nitrocresols in wastewater from the washing of DNT by sodium carbonate by precipitation. Nitrocresol is concentrated to a content of about 1% nitrocresol by circulation of the alkaline wash solution. Nitrocresol is precipitated by subsequent acidification of this concentrated alkaline wash solution with sulfuric acid to pH 1 or below, or the waste acid and nitrocresol are separated and disposed of by incineration. However, this process leads to the reduction of toxic substances in the wastewater, but does not completely remove them from the wastewater. In addition, the content of the inorganic salts is greatly increased so that wastewater streams contaminated with nitrocresol which, albeit in reduced amounts, have to be continuously withdrawn and further treated.

US 4 482 769 describes a further process for reducing the content of nitrocresol in alkaline wash water from washing of crude DNT. Trinitrocresol dissolved in crude DNT is selectively washed out in an alkaline wash at a pH of about 6, but dinitrocresol remains in DNT. The burden of toxic nitrocresols in the wastewater to be treated resulting from the DNT cleaning is thereby significantly reduced. Dinitrocresol remaining in DNT does not interfere with the reduction of DNT to the corresponding amine.

In both of these processes, only partial removal of the nitroaromatics and nitrocresols present in the wash water is achieved. This waste water is thus still heavily contaminated after removal of some of the toxic impurities, requiring further complex aftertreatment before discharge to the outflow drain.

Chimia 21,356-360 (1967), R. Angst and M. Brem, describes a process for purifying nitrocresol containing wastewater from nitration of toluene to form TNTs by treatment with activated carbon. According to these authors, microbiological purification of wastewater in combination with in-house wastewater does not result in any change in toxicity and color, and the wastewater is successfully discolored by treatment with activated carbon. The disadvantage of treatment with activated carbon is the high consumption of activated carbon, since activated carbon loaded with nitroaromatics and nitrocresol cannot be thermally regenerated for safety reasons due to the explosiveness of TNC and nitroaromatics, or nitroaromatics with an appropriate solvent This is because it can only be partially removed from the activated carbon again by extraction.

DE 1 221 994 and DE 1 222 904 describe a process for removing toxic nitrocresol from wash water from washing of MNT and DNT, in which nitrocresol is removed from the wastewater above pH 7 by a strong base exchange resin. To regenerate the exchange resin, it is treated with acid and acetone or other suitable solvent. Acetone loaded with nitrocresol is recovered by distillation and subsequent destruction of nitrocresol.

A further process described in many patents is the extraction of wastewater from scrubbing and steam from concentration of the final acid with the aromatics which have to be nitrated.

US 4 925 565 describes a process for extracting nitrophenol containing and / or nitrocresol containing wastewater with toluene. At pH about 1, three stage countercurrent extraction substantially removes nitrocresol from the wastewater. Toluene is recovered in the distillation unit and recycled to the extraction. The mixture of nitroaromatic / nitrocresol obtained at the bottom of the column is incinerated. Wastewater containing traces of nitrophenol is treated with activated charcoal after stripping and before discharge to the outflow duct.

US 3 742 072 removes all neutral nitro molecules, such as DNT and TNT, by extraction with toluene from “Mahon water” (wash water from off-gas scrub of TNT plants, specifically SAC plants). And recycling the loaded toluene from extraction to nitration.

EP 1 003 710 discloses acid cleaning of nitroaromatics, preferably DNT, with aromatics (toluene) which have to be nitrated in order to remove the nitroaromatics dissolved in acidic wash water before further treatment of the wastewater, such as concentration. Described is a process for extracting wastewater from. The extractant loaded with extracted nitroaromatics is recycled to nitration.

US 6 506 948 provides for the separation of neutral nitro molecules such as DNT by extraction of individual wastewater from the plant to produce DNT (vapor condensate, acid and finally alkaline wastewater) comprising toluene in countercurrent, A process for recycling to nitration with toluene is described. Further decomposition of the wastewater containing only nitrocresol is now carried out to remove the nitrocresol, so that neutral nitro molecules no longer interfere.

IT 912500 and CS 206 757 are removed from the combined wash water from the cleaning of the nitroaromatics by the extraction of the nitrocresols as well as the neutral nitroaromatics such as DNT and MNT to aromatic compounds which should be nitrated at pH values below 5 It describes the process to make. These nitrophenols are obtained as a highly concentrated solution by back extraction from the extractant with alkali, and after acidification, the nitrophenols are separated from this solution and passed through incineration. The extractant, i.e. the aromatics which have to be nitrated, is recycled to the nitration with the extracted DNT.

EP 1 493 730 and EP 1 496 043 also from the production of DNT, including waste water from acid washing and alkali washing of DNT, and steam condensation from concentration of MNT final acid with MNT / DNT content of 0.7-13% The partial purification process of the combined wastewater is described. The pH of this combined wastewater should be less than 5 as a result of proper combination of the various wastewater streams. Up to 90% of the nitrocresol and nitrobenzoic acid suspended in the combined wastewater are extracted by the MNT / DNT phase which is separated from the vapor condensate from the SAC plant in the separator. MNT / DNT mixtures having a separated content of nitrocresol and nitrobenzoic acid, such as 13.8% by weight, are disposed of by incineration or nitrocresol is oxidatively decomposed by a mixed acid suitable for this purpose (EP 1 493 730). The wastewater obtained after the MNT / DNT phase is separated off can be further extracted with toluene, from which the MNT and DNT still dissolved in the combined wastewater and the additional portion of nitrocresol still dissolved in the wastewater are removed therefrom. Toluene extract is recycled to nitration. Partially purified wastewater obtained after extraction with toluene, which may still contain up to 200 ppm of nitrocresol, cannot be directly discharged and must be further treated before discharge into the effluent discharge duct.

All these processes, the concentration of contaminants present in the wastewater and their subsequent disposal combined with only partial removal of impurities from individual or combined wastewater streams from the DNT, are technically complex, requiring additional chemicals, The acidification of the alkaline wash liquor and the back neutralization to a pH of about 7 results in an additional salt burden in the waste water.

In order to avoid this technically complex concentration technique, a process has been developed in which contaminants, in particular nitrocresol, are disposed of by chemical cracking without intermediate concentration of individual or combined wastewater streams.

EP 0 962 446 describes a process for partial removal of nitroaromatics and nitrocresols dissolved in alkaline wastewater by oxidation with nitric acid. The presence of up to 4% by weight of sulfuric acid and up to 4% by weight of nitric acid and a subsequent heating up to 180 ° C., resulting in the decomposition of nitrocresol and a substantial portion of dissolved DNT in the originally alkaline wastewater from the cleaning of the DNT Happens. The TOC of alkaline wastewater is reduced by 50% or less. The resulting partially purified wastewater must be passed through further treatment, such as treatment with activated carbon or biological treatment.

US 4 604 214 and US 5 356 539 describe a process for decomposing nitrocresol dissolved in alkaline wash water from washing of DNT with hydrogen peroxide in the presence of iron (II) salt (Fenton's reagent). Nitrocresol is concentrated to a content of about 1% by weight with multiple circulations of alkaline wash water. To treat this alkaline wash water, it is acidified to a pH of 4.5, preferably less than 3, mixed with a sufficient amount of hydrogen peroxide (7-12 mol / mol TNC) and iron salt and at a temperature of 70-90 ° C. Decompose More than 90% nitrocresol and about 50% dissolved DNT are decomposed to an average residence time of about 45 minutes in a continuous reactor. Here too, only partial purification of the alkaline washing water takes place. The residual content of nitrocresol up to 200 ppm in the wastewater treated in this way should be reduced to such an extent that the discharge to the sewer drainage is possible by further means, such as treatment with activated charcoal, in accordance with applicable current standards.

Apart from oxidation by hydrogen peroxide, ozone has also been used in targeted ways as an oxidant for the decomposition of nitrocresols in alkaline wash water from DNT plants.

EP 0 634 365 describes the use of ozone after removal of neutral nitro molecules from alkaline nitrophenol containing wash water in nitrobenzene plants. EP 0 953 546, paragraph 0007 describes a combination process comprising adsorption of water treatment sludge for partial removal of DNT, biological pretreatment, ozonation and biological post treatment of wastewater from nitrocresol from the DNT plant. Water treatment sludge loaded with DNT is incinerated.

When using an oxidizing agent such as nitric acid, hydrogen peroxide or ozone, complex biological intermediate purification and final purification steps are required, although complex intermediate concentrations of toxic constituents, such as nitroaromatics and nitrocresols, from the alkylation cleaning of crude DNT prior to disposal are unnecessary. Consuming additional oxidants with is complex, burdensome and expensive.

EP 0 581 229 describes salts in the presence of additional oxidants such as oxygen or air, below the supercritical temperature range for water at 325-370 ° C., but with the oxidant completely dissolved in the waste water and present in the waste water and formed by oxidation. Alkaline, which still contains all the nitro molecules and nitrocresols from the DNT cleaning, at supercritical pressures of 220-325 bar, where (carbonates) remain dissolved and are not precipitated by the evaporation reaction (thus preventing thermal decomposition) Wet oxidation of wastewater is described. The residence time required for oxidative decomposition is short. The waste water is still yellow after pyrolysis in the presence of oxidant and must be worked up before discharge to the outflow drain.

To avoid the additional consumption of expensive auxiliaries such as acids, bases and oxidants in the intermediate purification step and in the removal of biodegradable nitro molecules and nitrophenols in wastewater from the production of DNT, these disadvantages, in particular the addition of auxiliaries, Further described are processes that avoid consumption.

EP 0 005 203 describes a thermal cracking process for the direct treatment of alkaline wastewater comprising nitrocresols from nitration plants for the production of DNT, which requires no further chemicals or other intermediate steps. Wastewater from the alkaline cleaning stage of the DNT plant, free from neutral nitroaromatics such as DNT, is treated directly for 15 minutes excluding air and oxygen at 290-300 ° C. and at a pressure of about 100-110 bar. After cooling to room temperature, all sodium salts of nitrocresol were decomposed to CO ₂ , CO, nitrogen and other short chain decomposition products of nitrocresol.

EP 0 953 546 even describes a process that enables the implementation of thermal decomposition in the presence of neutral nitro molecules such as DNT in wastewater from the alkaline washing stage of a DNT plant. Complex removal of nitroaromatics without hydroxyl groups, such as nitrotoluene or dinitrotoluene, by extraction or steam stripping before introduction into the thermal decomposition is omitted.

EP 1 132 347 describes thermal decomposition in the supercritical range for pre-concentrated alkaline wash water from washing nitrobenzene. Preliminary concentration of the steam volatile nitroaromatics dissolved in the wash water, in this case most of the nitrobenzene, is separated from the wash water. Only the dissolved nitrophenols remain as salts and decompose completely at 500-600 ° C. and 25 MPa (250 bar). The distillate from the preconcentration is recycled to the wash. Wastewater from pyrolysis contains only a small amount of organic impurities and can be worked up in a water treatment plant.

Alkaline wastewater streams from the cleaning of DNT in alkaline scrubbing stages typically have nitrocresol and DNT removed after thermal decomposition, but are often dark due to colloidal precipitated carbon and are derived from DNT and nitrocresol Apart from low molecular weight decomposition products of unknown composition, ammonia, newly formed sodium carbonate and traces of dissolved CO are included. Compared to untreated water, TOC was reduced by about 20% and COD by about 30-35% pyrolysis. It is surprising that mononitroaromatics, such as MNT, decompose considerably slower than dinitroaromatics and trinitroaromatics, and nitrobenzoic acid does not degrade substantially at all under thermal decomposition conditions and remains unchanged in the wastewater. Therefore, this wastewater from pyrolysis must be post-treated, for example in a water treatment plant, in order to comply with applicable regulations in terms of color, COD, TOC and toxicity before discharge to the outflow drain.

Treatment in the thermal decomposition of wastewater which contains neutral nitroaromatics such as DNT and more toxic nitrophenols and nitrocresols and which can not be biodegradable or can only be biodegraded very difficult is very effective, but technically complex and expensive.

All the processes, apparatuses and measures described above for the treatment of wastewater from the production of DNT, particularly wastewater contaminated with toxic and difficult or impossible to decompose nitrocresol from the cleaning of DNT by alkali, are carried out in two steps, namely

a) removal of as much of the dissolved DNT and toxic nitrocresol as possible in water,

b) post-treatment of the wastewater preliminarily purified according to a) prior to the final discharge to the effluent discharge pipe, for example in a water treatment plant or by treatment with an adsorbent.

It includes.

These processes and apparatus for the treatment of this wastewater contaminated with nitro molecules, in particular for the pretreatment according to a), are all technically complex, expensive in terms of capital cost and operation, require additional chemicals, are often acidified and Subsequent neutralization results in further contamination with the inorganic salts introduced into the wastewater which have to be treated. In addition, mixing of alkaline wastewater and acid from DNT cleaning for the purpose of separating nitrocresol at a pH value of less than 5 results in the generation of significant amounts of CO ₂ , which is a problem due to the intense foaming combined with significant offgas contamination. Cause

In addition, in order to reduce the contamination of the waste water from the rinsing of the crude DNT with toxic nitrocresol, some of the nitrocresol and nitrophenol remain in the product (DNT), which are separated off, and only after the hydrogenation of the DNT the "heavy end ( heavy end) " is also described for the formation of diaminotoluene (TDA).

US 2 976 320 and US 4 482 769 describe processes in which only a part of the nitrocresols and nitrophenols present in the crude DNT remain in the DNT (up to 500 ppm, preferably up to 200 ppm). This results in wastewater from washing, which also contains most of the "nitrophenol" present in the crude DNT. This wastewater has to be further treated according to the prior art prior to discharge into the outflow drain.

CA 1 034 603 describes a process for washing crude DNT only with water to remove as far as possible (more than 99.9%) minerals that adversely affect hydrogenation. Some of the nitrocresol dissolved in crude DNT remains in the DNT, which is separated in the TDA stage. Nearly 40% of the nitrocresols originally present in the crude DNT enter the wastewater. In addition, all mines originally present in the crude DNT are dissolved in this wastewater. Not only the nitrate, but also the remaining nitrocresol, must be removed from this washing water in a complicated manner according to the prior art, before it is discharged into the outlet pipe.

US 4 224 249 discloses a process for hydrogenating DNT containing only incompletely washed with water, using Raney nickel to form diaminotoluene (TDA) and containing residual acid (up to 6000 ppm as sulfuric acid or up to 7700 ppm as nitric acid). List it. However, as the examples show, after only a short time the activity of the catalyst is reduced to zero at a residual acidity of about 6000 ppm in the washed DNT in the presence of about 800 ppm of nitrocresol. In addition, about one third of the "nitrophenol" originally present in the crude DNT enters the wash water in the wash (which is not described in more detail), and according to the prior art described above, It must be removed in a complex way.

An object of the present invention is a method for cleaning a dinitrotoluene-containing crude mixture obtained after the separation of nitric acid from nitration of toluene, which is a complex intermediate for separating or destroying nitrocresol and nitrobenzoic acid that are directed to the biological treatment stage of a water treatment plant. It is to provide a method for directly draining wastewater from this washing without treatment. Wastewater treated in a biological stage must be able to be introduced into the effluent discharge line while complying with all relevant legal requirements, such as the provisions of the waste water discharge regulations of the Federal Republic of Germany. In particular, it is an object of the present invention to provide a method for cleaning a DNT-comprising crude mixture, wherein the nitrobenzoic acid (mononitrobenzoic acid and dinitrobenzoic acid) present in the DNT-comprising crude mixture does not enter the wastewater from the washing. It is a further object of the present invention to also provide this type of process in which the content of nitric acid and sulfuric acid in the crude mixture containing DNT is minimized and at the same time the waste water contamination with sulfates and nitrates is minimized. A further object of the invention is that after washing, it may interfere with catalytic reduction of DNT to hydrogen, such as hydrocyanic acid (HCN), nitrous oxide (N ₂ O), nitrogen oxides (NO _x ) and carbon monoxide (CO). It is to provide a process of this type in which "industrial grade DNT" is obtained after washing, in which the potential catalytic poisons from oxidative degradation and known degradation products from the oxidative degradation in the DNT stage of nitration are minimized.

The object is to clean the crude mixture comprising dinitrotoluene, nitric acid, nitrogen oxides and sulfuric acid obtained after the separation of nitric acid from nitration of toluene, comprising two washing steps (WS-I) and (WS- II), where

i) In a first cleaning step (WS-I), the crude mixture is extracted with a cleaning acid I comprising nitric acid, nitrogen oxides and sulfuric acid by a cleaning comprising at least one extraction stage, wherein the first cleaning step (WS-I) The washed acid discharged from the first extraction stage (WS-I-1) of I) has a total acid content of 20 to 40% by weight, and a pre-washed dinitrotoluene-containing crude mixture is obtained.

ii) in a second washing step (WS-II), the pre-cleaned crude mixture is extracted with washing acid II by washing comprising at least one extraction stage, wherein the first of the second washing step (WS-II) The washing acid discharged from the extraction stage (WS-II-1) is achieved by a method in which a mixture comprising dinitrotoluene having a pH of 4 or less and substantially free of nitric acid and sulfuric acid is obtained.

The crude mixture may further comprise trace amounts of hydrocyanic acid, nitrous oxide and carbon monoxide.

The acid wash according to the invention comprising a first washing step (WS-I) and a second washing step (WS-II) is carried out in a second washing step to nitrocresol (dinitrocresol and to the biological treatment stage of the water treatment plant. It has surprisingly been found to provide wastewater which can be introduced without the intermediate treatment for the separation of trinitrocresol) and nitrobenzoic acid (mononitrobenzoic acid and dinitrobenzoic acid) and also oxidative degradation products of dinitrocresol. Wastewater obtained after discharge from the biological treatment stage can be discharged directly, in accordance with the limits set forth in the relevant legal requirements, for example the limits of the Federal Republic of Germany. In particular, when the pH value matches the value in the first extraction stage of the second washing step, it is surprising that substantially the entire amount of nitrobenzoic acid remains in the DNT containing organic phase and does not enter the wastewater.

At the same time, the contamination of waste water with nitrate, which can only be difficultly removed from the waste water, is significantly reduced compared to the prior art described for example in US 2 976 320, US 4 482 769 and CA 1 034 603.

The method of the present invention represents a further development of the most useful technique (BAT) as described in the BREF (BAT Reference) with regard to the EU directive on the integration reduction and avoidance of environmental pollutants (IRE-D). The process of the present invention not only makes it possible to significantly reduce the total amount of wastewater from the DNT plant, but also omits comprehensive and technically complex measures for the removal or partial removal of nitrocresol, nitrobenzoic acid and other decomposition products from the wastewater. have.

In the first washing step (WS-I) of this method, sulfuric acid and nitric acid, which are minerals dissolved in the crude product containing DNT, and also nitrogen oxides, are separated in one or more stage extraction using the washing acid as extractant.

The first rinse step is preferably carried out in at least two stages and countercurrent. Two or more single countercurrent extractions can in principle be carried out as described in EP 0 279 312, EP 0 736 514 or EP 1 780 195.

In countercurrent, the second cleaning step is generally carried out as follows:

I) In the first extraction stage (WS-I-1) of the first washing step (WS-I), a crude mixture comprising dinitrotoluene, nitric acid, nitrogen oxides and sulfuric acid belongs to this first extraction stage. With the circulated rinse acid (WA-I-1) from the first phase separation device (SI-1) and the excess rinse acid (WA-I-2) from the subsequent extraction stage (WS-I-2), The washing emulsion (WA-I-1) and the once washed crude mixture (DNT-I) were fed to the first mixer (MI-1) and the washing emulsion formed in the mixer in the first phase separation apparatus (SI-1). -1),

II) In the subsequent extraction stage (WS-I-2) of the first washing stage (WS-I), the once washed crude mixture (DNT-I-1) is subjected to a second phase separation apparatus belonging to this extraction stage. Circulated washing acid (WA-I-2) from (SI-2), and subsequent extraction stage (WS-I-3) if the first washing stage (WS-I) comprises more than two extraction stages Excess washing acid (WA-I-3), or a second mixer (MI-2) belonging to this extraction stage, together with fresh water or washing acid, if the first washing stage comprises exactly two extraction stages. If the first rinse step comprises more than two extraction stages, further extraction steps corresponding to steps I) and II) can be followed.

Countercurrent extraction can have up to n extraction stages. Here, the extractant is supplied to the end of the nth extraction stage WS-I-n of the first cleaning step WS-I. The introduced extractant, fed to this last extraction stage, may be a wash acid or fresh water with a certain total acid content. In an embodiment of the invention, the extractant introduced is water. In a further embodiment, the extractant introduced is a washing acid having a total acid content of 0.2-1.5% by weight. For example, this washing acid may be a vapor condensate from concentration of the washing acid obtained in the first extraction step WS-I-1 of the first washing stage WS-I. It generally comprises up to 1.0 wt% nitric acid and up to 0.3 wt% sulfuric acid.

The cleaning acid obtained in the first cleaning step of the first extraction stage generally has a total acid content of 20-40% by weight. This total acid content is the sum of nitric acid, sulfuric acid and nitrogen oxides, which is calculated as nitrous acid HNO ₂ .

The washing acid obtained in the first washing step in the first extraction stage can be recycled to nitration of toluene either directly or after concentration. It may also be introduced in the concentration of the final acid from the first stage of toluene nitration (mononitrotoluene (MNT) stage). In this first cleaning step (WS-I), the loading of the waste water obtained in the second cleaning step into sulfate and nitrate is substantially minimal. Only complex denitrification steps can remove nitrate from the wastewater.

The pre-cleaned DNT-comprising crude mixture obtained after the first rinse step generally has a sulfate content of at most 300 ppm, preferably at most 100 ppm, particularly preferably at most 50 ppm and a content of nitric acid and nitrogen oxides of at most 5000 ppm. It is preferably at most 3000 ppm, particularly preferably at most 1000 ppm.

 In the second rinse step (WS-II), the remaining residues of nitric acid, nitrogen oxides and sulfuric acid are extracted by one or more stage extraction into a rinse acid having only a low content of total acid (substantially nitric acid, nitrogen oxides and sulfuric acid). Rinse from the pre-cleaned DNT-comprising crude mixture, to a minimum to the content of mineral and nitrogen oxides in the DNT-comprising crude mixture.

The second washing step is preferably carried out in two or more stages and countercurrent. Countercurrent extraction can have m extraction stages. Here, the extractant is supplied to the end of the m th extraction stage WS-II-m of the second washing step WS-II. The extractant introduced is generally fresh water.

In countercurrent, the second cleaning step is generally carried out as follows:

I) In the first extraction stage (WS-II-1) of the second washing stage (WS-II), a pre-cleaned crude mixture comprising dinitrotoluene is added to a first phase separation apparatus belonging to this extraction stage ( To this extraction stage together with the circulated washing acid (WA-II-1) from S-II-1) and excess washing acid (WA-II-2) from the subsequent extraction stage (WS-II-2). The cleaning emulsion formed in the first mixer was supplied to the first mixer (M-II-1) belonging to the cleaning acid (WA-II-1) and washed once in the first phase separation apparatus (S-II-1). Separate with crude mixture (DNT-II-1),

II) In the subsequent extraction stage (WS-II-2) of the second washing stage (WS-II), the once washed crude mixture (DNT-II-1) is subjected to the second phase belonging to this second extraction stage. Circulated washing acid (WA-II-2) from separation device (S-II-2), and subsequent extraction stage (WS-II) if the second washing stage (WS-II) comprises more than two extraction stages. Excess wash acid (WA-I-3) from I-3) or a second mixer (M-II-) belonging to this extraction stage with fresh water if the washing stage comprises exactly two extraction stages. 2) supplies

Here, if the second cleaning step comprises more than two extraction stages, further extraction steps corresponding to steps I) and II) can be followed. Here, the second washing step is carried out such that substantially no more than 95% by weight of the nitrocresol and nitrophenol, preferably nitrobenzoic acid originally present in the crude mixture remains in the crude mixture and is not discharged with the washing acid. This is achieved according to the invention by the washing acid discharged from the first extraction stage WS-II-1 of the second washing step WS-II having a pH of 4 or less. In low concentration washing acids with a pH of 4 or less and discharged as waste water, the total content of nitrocresol and nitrophenol is generally less than 5 ppm and the content of nitrobenzoic acid is generally less than 50 ppm. This wastewater, which now comprises a washed DNT in dissolved form only below its saturation limit, is directly or dissolved in a water treatment plant without pretreatment which has previously required to remove conventional, nitrocresol and nitrobenzoic acid and also toxic oxidative degradation products. The recovered DNT can be supplied after recovery.

In each of the two cleaning steps (WS-I) and (WS-II), the washing is preferably carried out in two or more stages in countercurrent. In one embodiment, the first rinse step (WS-I) comprises two to four extraction stages (n = 2-4). In a further embodiment, the second rinse step (WS-II) comprises two to four extraction stages (n = 2-4). It is also possible to provide more extraction stages, such as five or six extraction stages per cleaning step. In one embodiment, each cleaning step comprises exactly two extraction stages.

The amount of extractant or fresh water added in the last extraction stage of each washing stage is determined by the total acid content (WS-I) or pH required in the first extraction stage of each washing stage (WS-I) or (WS-II). (WS-II).

The volume ratio of the crude mixture comprising DNT (organic phase) to the cleaning acid (aqueous phase) in direct contact with each other in each cleaning device is generally 1: 4 to 10: 1, preferably 1: 3 to 5: 1 in both cleaning steps. , Particularly preferably 1: 3 to 2: 1. Depending on the phase ratio and energy input during dispersion, the mixture may be present as an oil-in-water emulsion (0 / W emulsion) or a water-in-oil emulsion (W / O emulsion).

These phase ratios can be set by circulating the washing acid after phase separation in the last extraction stage by introducing an appropriate amount of extractant, but preferably a predetermined amount of extractant, and only by excess (extractant newly introduced into the last extraction stage). Corresponding to the amount of is discharged from or introduced into the preceding extraction stage.

The pH of the washing acid withdrawn from the first extraction stage (WS-II-1) of the first washing step (WS-II) is generally in the range of 0 to 3, preferably 0.5 to 2, particularly preferably 0.8 to 1.2. . In the first extraction stage of the second cleaning stage, via the residual content of nitric acid in the precleaned crude mixture from the first cleaning stage and / or via the amount of fresh water introduced into the last extraction stage of the second cleaning stage. The predetermined optimal pH of can be set. As an alternative, the predetermined pH can also be set by addition of a mineral acid, such as a cleaning acid from the first cleaning step, or sulfuric acid or preferably nitric acid.

The ratio of DNT to fresh water introduced into the last extraction stage of the second washing step is 1: 2-15: 1 by volume (which corresponds to 1.5 m 3 -0.05 m 3 of fresh water per ton of DNT), preferably 1: 1- 7: 1 (corresponding to 0.75 m 3 -0.107 m 3 of fresh water per tonne of DNT), particularly preferably 1: 1 to 2: 1 (corresponding to 0.75 m 3 -0.38 m 3 of fresh water per tonne of DNT). . Both cleaning steps are carried out at temperatures above the melting point of the DNT, generally between 60 and 75 ° C.

As a cleaning device for both cleaning steps, for example, a mixer-setler device or a stirred multistage or pulsed pack column or sieve tray column, and also a static mixer can be used with a suitable separation device. Both static separators and dynamic separators (centrifugal separators) are suitable for the separation of the washing dispersion consisting of the washing mixture and the crude mixture comprising DNT to be cleaned.

washing withdrawn from the first extraction stage (WS-II-1) of the second washing step (WS-II) having a pH of 4 or less, preferably 0 to 3, particularly preferably 0.5 to 2, especially 0.8 to 1.2 Acids generally have a sulfate content of 100 ppm or less, a nitric acid content of 2000 ppm or less, and an HNO ₂ content of 50 ppm or less. It also includes isomer dinitrotoluene in an amount corresponding to the saturation limit at a given temperature, such as 800-1000 ppm. The content of nitrocresol and nitrophenol is generally less than 1 ppm and the content of nitrobenzoic acid is generally less than 50 ppm.

The TOC (total organic carbon) content of this wastewater is only about 1100 mg / l, compared to about 3000 mg / l in wastewater from alkaline DNT washes using, for example, sodium carbonate. This COD (chemical oxygen demand) of this wastewater is only about 3000 mg O / l compared to about 6000 mg O / l in wastewater, for example from alkaline DNT cleaning with sodium carbonate. This wastewater can be passed directly to the biological treatment stage of the water treatment plant after recovery of the dissolved DNT, either by extraction with toluene or without further pretreatment such as thermal decomposition or treatment with oxidants, and then generally DIN EN In terms of toxicity, including genotoxicity measured according to ISO 38415 T6 (fish), 11348-2 (luminescent bacteria), 38412 L30 (water flea), 38412 L33 (algae) and DIN EN ISO 9888 (Umu Test, genotoxicity) Meets all requirements of the wastewater regulation of the Federal Republic of Germany.

Generally, neutralize the washing acid discharged from the first extraction stage (WS-II-1) of the second washing step (WS-II) and optionally dissolve the dinitrotoluene dissolved therein by extraction and removal of the extractant. After removal, it can be fed to the biological treatment stage of the water treatment plant without further pretreatment.

Residual acidity is generally 300 ppm or less (measured as sulfuric acid), pH 2-4, generally 800 ppm or less nitrocresol and nitrophenol, 600 ppm or less nitrobenzoic acid (dinitrobenzo and mononitrobenzoic acid), and general Cyanide up to 300 ppm, preferably up to 200 ppm, particularly preferably up to 100 ppm nitric acid (NO _x , measured as nitric acid), up to 50 ppm, preferably up to 10 ppm, particularly preferably up to 1 ppm Hydrogen acid, 200 ppm or less, preferably 50 ppm or less, particularly preferably 25 ppm nitrous oxide, 400 ppm or less, preferably 200 ppm or less, particularly preferably 50 ppm or less CO, and 3 ppm or less sulfate The DNT containing the residual content of is withdrawn from the last extraction stage of the second washing step (WS-II). This DNT and nitrocresol, nitrophenol, nitrobenzoic acid and trace amounts of NO _x , hydrocyanic acid, nitrous oxide and CO dissolved therein completely and toluenediamine (TDA) and the corresponding aminocresol, aminophenol and aminobenzoic acid (diamino Hydrogenation without problems arising in a manner corresponding to the prior art for forming benzoic acid and monoaminobenzoic acid). Aminocresol, aminophenol and aminobenozoic acid remain in the distillation residue in TDA distillation and are disposed of with this.

A further advantage is that the thermal stability of DNT subjected to acid cleaning according to the invention is greater. Thus, compared to DNT, which is washed according to the prior art in the presence of sodium carbonate and which comprises, for example, less than 20 ppm nitrophenol and nitrocresol, the temperature at which thermal decomposition is initiated is subjected only to acid washing, for example 620 ppm of nitrophenol and nitrocresol. And about 20 ° C. for DNT comprising 460 ppm of nitrobenzoic acid.

1 schematically depicts the cleaning of crude DNT by the process of the invention according to a preferred embodiment of the invention.

The crude DNT from nitration after removal of the DNT final acid (C-DNT) was removed from the phase separation apparatus (SI-1) in washing step I (WS-I), so that the prescribed phase of washing acid to DNT was ensured. The first extraction stage (WS-I-1) with excess circulating washing acid (WA-I-1) and excess washing acid (WA-I-2) from the subsequent extraction stage (WS-I-2) It is supplied to the mixer MI-1 of n = 1). After phase separation of the washing emulsion in the phase separation apparatus S-I-1 belonging to the extraction stage, the separated washing acid WA-I-1 is recycled to the mixer M-I-1 belonging to this stage. Excess wash acid (WA-I-1) is recycled to nitration either directly or after concentration.

Once washed DNT (DNT-I-1), separated in separator (SI-1), the circulated washing acid (SI-2) of the phase separation device (SI-2) is ensured so that the prescribed acid to clean acid to DNT WA-I-2) and the mixer of the subsequent extraction stage (WS-I-2) (n = 2) with excess washing acid (WA-I-3) from the subsequent extraction stage (WS-I-3) MI-2). After phase separation of the washing emulsion in the phase separation device (S-I-2) belonging to this extraction stage, the separated washing acid (WA-I-2) is recycled to the mixer (M-I-2) belonging to this stage. Excess wash acid (WA-I-2) is fed to the preceding extraction stage (WS-I-1). The twice washed DNT (DNT-I-2), separated in the phase separation device (S-I-2), is transferred to the next extraction stage (WS-I-3) (n = 3) for a third wash. The fresh water from the concentration of the cleaning acid from the cleaning stage (WS-I-1) or preferably the vapor condensate is the cleaning medium (W-1-1), the amount of the cleaning acid separated from (SI-1) The final extraction stage (WS-I-4) is fed to have a total acid content of 20-40%.

The pre-cleaned DNT (DNT-In) from the cleaning step (WS-I) is subjected to a phase separation apparatus (S-II-1) such that in the washing step (WS-II), the prescribed phase of the cleaning acid to the DNT is ensured. The first extraction stage (WS-II-1), with the circulated washing acid (WA-II-1) from and the excess washing acid (WA-II-2) from the subsequent extraction stage (WS-II-2) ) is supplied to the mixer (M-II-1) of (m = 1). After phase separation of the washing emulsion in the phase separation apparatus (S-II-1) belonging to the washing stage, the separated washing acid (WA-II-1) is recycled to the mixer (M-II-1) belonging to this stage. . Excess wash acid (WA-II-1) is fed directly or after recovery of the product (DNT) dissolved therein to the final biological workup.

Single-washed DNT (DNT-II-1), separated in phase-separator (S-II-1), to ensure the prescribed phase of wash acid to DNT, phase-separator (S-II-2) Subsequent extraction stage (WS-II-2), with circulated washing acid from (WA-II-2) and excess washing acid (WA-II-3) from subsequent washing stage (WS-II-3) It supplies to the mixer (M-II-2) of (m = 2). After phase separation of the washing emulsion in the phase separation apparatus (S-II-2) belonging to this extraction stage, the separated washing acid (WA-II-2) is recycled to the mixer (M-II-2) belonging to this stage. Let's do it. Excess wash acid (WA-II-2) is fed to the preceding extraction stage (WS-II-1). The twice washed DNT (DNT-II-2), separated in the phase separation device (S-II-2), is transferred to the next extraction stage (WS-II-3) (m = 3) for a third wash. The number of extraction stages may preferably be 4 (m = 4) or less. The fresh water is used as the washing medium (W-11-1), and in an amount such that the washing acid separated from (S-II-1) preferably has a pH of 0 to 3, to the final extraction stage (WS-II-4). Supply. The addition of nitric acid or washing acid (WA-I-1) may further readjust the pH in the first washing stage (WS-II-1) to the optimum operating value.

Figure 2 schematically shows a production plant according to the invention for the nitration of toluene to form DNT, using the subsequent washing according to the invention of the crude DNT in two stages according to a preferred embodiment of the invention.

Nitrogenation in a phase separation apparatus (separator S) with dinitrotoluene isomeric mixture formed by two stages of continuous isothermal or adiabatic nitration of toluene to countercurrent, with a mixture of sulfuric acid and nitric acid in the nitration unit (N) After separation of the emulsion, it is fed to a wash according to the invention with two washing steps (WS-I) and (WS-II). In the cleaning step (WS-I), the sulfuric acid, nitric acid and nitrogen oxides dissolved in crude DNT are washed off. In this washing step, the washing acid (WA-I-1) having a total acid content of 20 to 40% by weight, separated from the first washing stage (WS-I-1), is added directly or to the nitration unit (N). After concentration of the solution is recycled to nitration as (NA-2). Vapor condensate from the washing acid (WA-I-1) and / or the concentration of the final nitrovolcano is recycled to the washing step (WS-I) as washing water (W-1).

In the second washing step (WS-II), the residue of the mine still remaining in the pre-cleaned DNT from (WS-I) is washed acid (WA-II-1 having a pH preferably in the range of 0 to 3). Rinse in such a way as to produce). To make up for the amount of separated wash acid, fresh water is added in (WS-II). The pH of this washing acid from washing step II (WS-II) is brought to 6-8, followed by the recovery of DNT directly or dissolved therein, followed by biological post-treatment of the water treatment plant (WTP).

The final nitroacid obtained in separation unit (S) is reconcentrated to give sulfuric acid (up to 96%) in a concentrated plant (SAC) for sulfuric acid, which is recycled to nitration. Nitric acid (NA-1) recovered in offgas treatment (OT) from collected offgas including nitrogen oxides from nitration and scrubbing was washed acid (WA-I-1) obtained from scrubbing step (WS-I) ) Or after concentration and recycle to nitration as (NA-2).

The invention is illustrated by the following examples.

Example

Example 1 (Prior Art)

4500 kg / h of DNT having a residual content of 0.94% by weight sulfuric acid, 1.43% by weight nitric acid and 1.15% by weight nitrogen dioxide was washed in a two-stage countercurrent after removal of the final nitroacid in the acid wash (Washing step I) It was. In the first extraction stage, a washing acid comprising 7.58 wt% sulfuric acid, 19.52 wt% nitric acid and about 0.45 wt% nitrogen oxides (as HNO ₂ ) is used to wash at an aspect ratio of DNT to washing acid of 1: 1. Was carried out. In the second extraction stage of washing step I, the washing was likewise carried out in a phase ratio of 1: 1 using a washing acid comprising up to 0.5 wt% sulfuric acid, about 6 wt% nitric acid and about 0.15 wt% nitrogen oxides. . The amount of water or condensate addition (about 450 l / h in this example) from the further concentration of the cleaning acid fed to the last extraction stage is brought into contact with the crude DNT which is to be cleaned in the first extraction stage of the acid cleaning. The concentration of was chosen so as not to exceed the defined acid strength and density. To maintain the prescribed ratio, the separated wash acid was circulated in the separator (phase separator) of each extraction stage, and only excess was transferred or discharged to the preceding washing stage.

The washed acid with a total acid content of 27.55 40% by weight from the acid washed was further concentrated and recycled to nitration.

The residues of the washed acid still dissolved or captured in the pre-cleaned DNT and the nitrophenol and nitrocresol in the alkaline wash in the DNT from the acid wash, substantially free of acid, were removed.

About 4350 kg of pre-cleaned DNT from washing step I (acid washing) with residual content of sulfuric acid below 100 ppm and nitric acid / nitrogen oxide below 3000 ppm was subjected to base (sodium carbonate) in alkaline washing step (alkali washing). Washing at a phase ratio of 1: 1 in one stage while establishing a pH of 9-10 in the presence of. After phase separation of the washing emulsion from alkaline washing, the separated DNT was likewise washed in a phase ratio of 1: 1 to remove captured traces from alkaline washing by addition of fresh water in a single stage neutral wash. After phase separation, the washing water separated in the neutral washing was supplied to the alkaline washing as washing water. To maintain the prescribed ratio in the two cleaning steps (alkaline cleaning and neutral cleaning), the separated washing water is circulated in the separator of each cleaning stage and only the excess is transferred from neutral cleaning to alkaline cleaning, or alkaline cleaning. Was discharged from.

The alkaline cleaning liquid discharged from alkaline cleaning having a pH of 9-10 and having a content of 40 ppm sulfate, 580 ppm nitrate, 2500 ppm nitrite, 990 ppm DNT and 740 ppm trinitrocresol was subjected to 290 ° C. and 90 bar. Direct feeding to pyrolysis in to decomposes nitrophenols and nitrocresols and also further nitro compounds and dissolved DNTs. Nitrophenol and nitrocresol and dissolved DNT were subjected to biological post-treatment of the water treatment plant prior to draining the water flowing from the destroyed pyrolysis into the effluent outlet.

Example 2 (according to the invention)

4500 kg / h of DNT having a residual content of 0.94% by weight sulfuric acid, 1.43% by weight nitric acid and 1.15% by weight nitrogen dioxide was subjected to countercurrent in two stages after removal of the final nitroacid in washing step I (WS-I). Washed. In the first extraction stage (WS-I-1), 1: 1 DNT using a cleaning acid comprising 7.58 wt% sulfuric acid, 19.52 wt% nitric acid and about 0.45 wt% nitrogen oxides (as HNO ₂ ) The washing was carried out with an aspect ratio of washing acid. In the second extraction stage (WS-I-2) of the cleaning step I, a 1: 1 extraction is also performed using a cleaning acid comprising up to 0.5% by weight of sulfuric acid, about 6% by weight of nitric acid and about 0.15% by weight of nitrogen oxides. The washing was carried out at the ratio of. The amount of water or condensate addition (about 450 l / h in this example) from the further concentration of the cleaning acid fed to the last extraction stage is obtained from the crude DNT to be cleaned in the first extraction stage (WS-I-1). The concentration of the contacting washing acid was chosen so as not to exceed the defined acid strength and density. To maintain the prescribed ratio, the separated wash acid was circulated in the separator (phase separator) of each extraction stage, and only excess was transferred or discharged to the preceding washing stage.

The washed acid with a total acid content of 27.55% by weight from the acid washed step (WS-I) was further concentrated and recycled to nitration.

Of the cleaning acid from the precleaned DNT that completely removed the photoacid in the washing step (WS-I) from the washing step I (WS-I) still dissolved or captured in the DNT in the washing step II (WS-II) The residue was removed.

About 4350 kg of pre-cleaned DNT from washing step I (WS-I), with residual content of sulfuric acid up to 100 ppm and nitric acid / nitrogen oxide up to 2000 ppm, was washed in two stages of countercurrent. In the first extraction stage of washing step II (WS-II), washing was carried out using a washing acid having a pH of 0 to 3, particularly preferably 0.8 to 1.2, in a ratio of DNT: clean acid of 1: 2. In the second extraction stage of washing stage II (WS-II), washing was likewise carried out with a phase ratio of 1: 2 using only washing acid containing only trace amounts of minerals, in particular nitric acid. The amount of fresh water supplied to the final extraction stage (WS-II-n) (n = 2) (about 2000 l / h in this embodiment) is the first to which DNT from the washing step I (WS-I) is extracted. The pH at the extraction stage (WS-II-1) was chosen to maintain a defined optimal value in the range of 0.8-1.2. To maintain the prescribed ratio at the extraction stage, the wash acid separated in the separator of each extraction stage was recycled and only excess was transferred to the preceding stage or discharged.

Cleaning step II (WS-II) having a pH of 1.0 and having a content of 85 ppm sulfuric acid, 1800 ppm nitric acid, 40 ppm nitrogen oxide, 980 ppm DNT, less than 1 ppm trinitrocresol and less than 10 ppm nitrobenzoic acid ), The washing acid discharged from the first extraction stage (WS-II-1) was fed directly to the biological treatment. Wastewater obtained after this biological treatment fulfilled all the requirements relating to toxicity specified in the wastewater regulations of the Federal Republic of Germany.

Claims (15)

A method of washing a crude mixture containing dinitrotoluene, nitric acid, nitrogen oxides and sulfuric acid obtained by separating nitrating acid containing nitric acid and sulfuric acid from nitration of toluene,
Two cleaning steps (WS-I) and (WS-II), wherein
i) In a first washing step (WS-I) carried out in countercurrent, the crude mixture is extracted with washing acid I comprising nitric acid, nitrogen oxides and sulfuric acid by washing comprising at least two extraction stages, Here, fresh water or a washing acid having a total acid content of 0.2 to 1.5% by weight is supplied to the last extraction stage (WS-In) of the first washing step (WS-I), and the first washing step (WS-I) 1 The washing acid discharged from the extraction stage (WS-I-1) has a total acid content of 20 to 40% by weight, and a pre-cleaned crude mixture is obtained.
ii) In a second washing step (WS-II) in countercurrent, the pre-cleaned crude mixture comprising dinitrotoluene is extracted with washing acid II by washing comprising two or more extraction stages, wherein fresh water is removed. 2 The cleaning acid discharged from the first extraction stage (WS-II-1) of the second cleaning stage (WS-II) and the final extraction stage (WS-II-m) of the cleaning stage (WS-II) Is 4 or less, and a mixture comprising dinitrotoluene which is substantially free of nitric acid, sulfuric acid and nitrogen oxides is obtained, and the mixture is the last extraction stage (WS-II-m) of the second washing step (WS-II). ), Containing up to 300 ppm of nitric acid and nitrogen oxides and up to 3 ppm of sulfate,
n = 2-6, m = 2-6,
The cleaning acid discharged from the first extraction stage (WS-II-1) of the second cleaning step (WS-II) is composed of 100 ppm or less of sulfate, 2000 ppm or less of nitric acid, and 50 ppm or less of nitrogen oxide. Having a content (calculated as HNO ₂ ). The method of claim 1, wherein the first cleaning step (WS-I) comprises two to four extraction stages. The method of claim 1, wherein the second cleaning step (WS-II) comprises two to four extraction stages. The process according to claim 1, wherein the washing acid withdrawn from the first extraction stage (WS-II-1) of the second washing step (WS-II) has a pH of 0-3. The method of claim 1, wherein the washing acid withdrawn from the first extraction stage (WS-II-1) of the second washing step (WS-II) has a pH of 0.5-2. The process according to claim 1, wherein water or a cleaning acid having a total acid content of 0.2 to 1.5% by weight is fed to the last extraction stage (WS-I-n) of the first cleaning step (WS-I). The method of claim 1, wherein water is supplied to the last extraction stage (WS-II-m) of the second washing step (WS-II). The method of claim 1,
I) In the first extraction stage (WS-I-1) of the first washing step (WS-I), a crude mixture comprising dinitrotoluene, nitric acid, nitrogen oxides and sulfuric acid belongs to this first extraction stage. With the circulated rinse acid (WA-I-1) from the first phase separation device (SI-1) and the excess rinse acid (WA-I-2) from the subsequent extraction stage (WS-I-2), The washing emulsion (WA-I-1) and the once washed crude mixture (DNT-I) were fed to the first mixer (MI-1) and the washing emulsion formed in the mixer in the first phase separation apparatus (SI-1). -1),
II) In the subsequent extraction stage (WS-I-2) of the first washing stage (WS-I), the once washed crude mixture (DNT-I-1) is subjected to a second phase separation apparatus belonging to this extraction stage. Circulated washing acid (WA-I-2) from (SI-2), and subsequent extraction stage (WS-I-3) if the first washing stage (WS-I) comprises more than two extraction stages Excess washing acid (WA-I-3), or a second mixer (MI-2) belonging to this extraction stage, together with fresh water or washing acid, if the first washing stage comprises exactly two extraction stages. How to feed on. The method of claim 1,
I) In the first extraction stage (WS-II-1) of the second washing stage (WS-II), a pre-cleaned crude mixture comprising dinitrotoluene is added to a first phase separation apparatus belonging to this extraction stage ( To this extraction stage together with the circulated washing acid (WA-II-1) from S-II-1) and excess washing acid (WA-II-2) from the subsequent extraction stage (WS-II-2). The cleaning emulsion formed in the first mixer was supplied to the first mixer (M-II-1) belonging to the cleaning acid (WA-II-1) and washed once in the first phase separation apparatus (S-II-1). Separate with crude mixture (DNT-II-1),
II) In the subsequent extraction stage (WS-II-2) of the second washing stage (WS-II), the once washed crude mixture (DNT-II-1) is subjected to the second phase belonging to this second extraction stage. Circulated washing acid (WA-II-2) from separation device (S-II-2), and subsequent extraction stage (WS-II) if the second washing stage (WS-II) comprises more than two extraction stages. Excess wash acid (WA-I-3) from I-3) or a second mixer (M-II-) belonging to this extraction stage with fresh water if the washing stage comprises exactly two extraction stages. 2) How to feed. The process of claim 1 wherein the volume ratio of the dinitrotoluene containing crude mixture to the washing acid in the extraction stage of the washing steps (WS-I) and (WS-II) is from 1: 4 to 10: 1. The process of claim 1 wherein the volume ratio of dinitrotoluene containing crude mixture to fresh water in the last extraction stage (WS-II-m) of the second washing step (WS-II) is from 1: 2 to 15: 1. The mixture of dinitrotoluene comprising not more than 800 ppm of nitrocresol and nitrophenol and less than 600 ppm of nitrobenzoic acid is subjected to the last extraction stage (WS-II-) of the second cleaning step (WS-II). m) How to take out from. delete 2. The cleaning acid according to claim 1, wherein the cleaning acid discharged from the first extraction stage (WS-II-1) of the second cleaning step (WS-II) has a total content of nitrocresol and nitrophenol of less than 5 ppm, and less than 50 ppm. A method having a content of nitrobenzoic acid. The biological treatment stage of the water treatment plant according to claim 14, wherein the cleaning acid discharged from the first extraction stage (WS-II-1) of the second cleaning stage (WS-II) is neutralized and without further pretreatment. How to feed).

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